This invention relates to a method and an apparatus for removing a Ti-derived film coated on the surface of a cutting tool or the like.
In recent years, cutting tools having a Ti-derived film, such as a titanium nitride film or a titanium carbide film, coated on the surface of high speed tool steels for improved wear resistance have been in frequent use. In such a cutting tool, the film on a cutting part wears earlier than the film at other sites during use of the cutting tool. After a predetermined period of use, therefore, the film is entirely removed, and the cutting part is cut for readjustment. Then, a Ti-derived film is coated on the cutting tool for recycling. If the coated film deviates from the standard values during the Ti-derived film coating process, all the film is removed, and then the cutting tool is coated again for recycling.
Such removal of a Ti-derived film for recycling is disclosed, for example, in Japanese Unexamined Patent Publication No. 5-112885. According to a method for removing a titanium coated film disclosed in this publication, a cutting tool having a Ti-derived film (TiN, TiC, TiCN or Ti) coated on a base material of high speed tool steel is immersed (12 hours) at a temperature of 10 to 40xc2x0 C. in a mixed aqueous solution containing 1 to 20% by weight of a polymerized phosphoric acid alkali salt, 1 to 10% by weight of one or more of hydroxy carbonate-derived organic acid alkali salts, 2 to 15% by weight of an ethylenediamine-acetic acid alkali salt, 0.1 to 5% by weight of an alkali hydroxide, and 3 to 7% by weight of hydrogen peroxide. By so doing, the Ti-derived film is removed.
As noted above, with the method of titanium-coated film removal disclosed in the publication, the cutting tool coated with the Ti-derived film is immersed for a predetermined time (12 hours) in a predetermined mixed aqueous solution to remove the Ti-derived film. Removal of the Ti-derived film takes a long time (film removal rate: about 0.3 xcexcm/h), meaning a poor efficiency of treatment. Particularly in removing a TiAlN film, it cannot be removed even when immersing the cutting tool for 60 hours in the aqueous solution. In this case, the film removal rate is less than 0.1 xcexcm/h.
Under these circumstances, the present invention has as an object the provision of a method and an apparatus for removing a Ti-derived film, the method and apparatus being capable of efficiently removing the Ti-derived film coated on the surface of a member.
The present invention is a method for removing a Ti-derived film, which comprises immersing an electrode and a member coated with the Ti-derived film in a solution having an OHxe2x88x92 ion concentration of 102 to 10xe2x88x924 mol/l, and applying a positive potential to the member, and a negative potential to the electrode.
Thus, the Ti-derived film coated on the surface of the member can be removed efficiently.
The present invention is also the method for removing a Ti-derived film, wherein the solution is an aqueous solution containing an alkali hydroxide and having a pH of 10 or greater. Thus, removal of the Ti-derived film coated on the surface of the member can be performed easily.
The present invention is also the method for removing a Ti-derived film, wherein the temperature of the aqueous solution is kept at room temperature to the boiling temperature of the aqueous solution. Thus, the Ti-derived film coated on the surface of the member can be removed in a short time.
The present invention is also the method for removing a Ti-derived film, wherein the aqueous solution is kept at a predetermined temperature by initially raising its temperature by heating, and then raising its temperature by the heat of reaction. Thus, removal of the Ti-derived film can be performed from the start of the operation, and the surface of the member deprived of the Ti-derived film can be finished to be smooth.
The present invention is also the method for removing a Ti-derived film, wherein the solution is a solution of an alkali hydroxide melted in a solvent consisting of a molten salt and an organic solvent.
The present invention is also the method for removing a Ti-derived film, wherein the Ti-derived film is a film of titanium-aluminum nitride (TiAlN). Thus, the film of titanium-aluminum nitride (TiAlN) as the Ti-derived film can be removed reliably in a short time.
The present invention is also the method for removing a Ti-derived film, wherein the solution is an aqueous solution containing an alkali hydroxide and hydrogen peroxide.
The present invention is also an apparatus for removing a Ti-derived film, which comprises a tank holding a solution having an OHxe2x88x92 ion concentration of 102 to 10xe2x88x924 mol/l, an electrode immersed in the solution, and a power source for applying a positive potential to a member coated with the Ti-derived film, and applying a negative potential to the electrode.
Thus, the Ti-derived film coated on the surface of the member can be removed efficiently by a simple constitution.
The present invention is also the apparatus for removing a Ti-derived film, wherein the solution is an aqueous solution containing an alkali hydroxide and having a pH of 10 or greater, and the tank is provided with a heating means for heating the aqueous solution to a temperature in a range of from room temperature to the boiling temperature of the aqueous solution, and keeping the aqueous solution at this temperature. Thus, the operation of removing the Ti-derived film coated on the surface of the member can be performed easily and in a short time.